1. Technical Field
This invention relates to systems and methods for diagnosing Exhaust Gas Recirculation (EGR) valve performance.
2. Background and Summary
As is known in the art, internal combustion engines and more particularly internal combustion engines used on most passenger and truck vehicles use exhaust gas recirculation (EGR) systems to reduce exhaust pollution. As is also known in the art, diesel engines-typically incorporate EGR to reduce combustion temperature and the formation of NOx. Several techniques have been suggested to diagnose trouble within the EGR system. One such suggested method is in U.S. Pat. No. 5,239,971 entitled xe2x80x9cTrouble Diagnosis Device for Exhaust Gas Recirculation Systemxe2x80x9d inventor Uchinami issued Aug. 31, 1993. In such suggested system, a diagnostic device receives the output detected by one of the engine sensors and compares the output with a predetermined value of the same kind as the output a normal state of the EGR system corresponding to the engine condition detected by the sensors. Specifically, one of the sensors detects NOx in exhaust gas or exhaust gas temperature. More particularly, the suggested method diagnoses whether an EGR valve is stuck open or stuck closed. The diagnosis is based on an instantaneous NOx sensor reading compared with a predetermined high or low limit. If the instantaneous difference is greater/less than the limit, a malfunction illumination light (MIL) is triggered.
I have discovered that a more robust method for diagnosing the EGR valve is to process the NOx sensor readings using a statistical model. The use of such a statistical model reduces false indications of a faulty EGR valve. Further, my method enables determination of whether a sticky or loose EGR valve condition exists. Still further, my method enables determination of whether it is the EGR valve that is faulty rather than the NOx sensor being faulty.
In accordance with the invention, a method and system are provided for diagnosing a condition of an EGR valve used in an engine system. The EGR valve controls the portion of exhaust gases fed back to an intake of such engine system. The engine system includes a NOx sensor for measuring NOx in such exhaust. The method includes: determining a time rate of change in NOx measured by the NOx sensor; comparing the determined time rate of change in the measured NOx with a predetermined expected time rate of change in measured NOx; and determining the condition of the EGR valve as a function of such comparison.
In accordance with another feature of the invention, a method and system are provided for diagnosing a condition of an EGR valve used in an engine system. The EGR valve controls the portion of exhaust gases fed back to an intake of such engine system. The engine system includes a NOx sensor for measuring NOx in such exhaust. The method includes: determining from NOx measured by the NOx sensor and engine operating conditions indications of instances when samples of such measured NOx are greater than an expected maximum NOx level for such engine condition and less than an expected minimum NOx level for such engine condition; and determining the condition of the EGR valve as a function of a statistical analysis of such indications.
In accordance with yet another feature of the invention, a method and system are provided for diagnosing a condition of an EGR valve used in an engine system. The EGR valve controls the portion of exhaust gases fed back to an intake of such engine system. The engine system includes a NOx sensor for measuring NOx in such exhaust. The method includes: determining a time rate of change in NOx measured by the NOx sensor; comparing the determined time rate of change in the measured NOx with a predetermined expected time rate of change in measured NOx; and determining from the NOx measured by the NOx sensor and engine operating conditions indications of instances when samples of such measured NOx are greater than an expected maximum NOx level for such engine condition and less than an expected minimum NOx level for such engine condition.
In one embodiment, the method includes determining whether the NOx sensor is faulty and wherein the EGR condition determining includes in such determination the determination as to whether the NOx sensor is faulty.